Sensor arrangement consisting of light-sensitive and/or X-ray sensitive sensors

ABSTRACT

The invention relates to a large-area sensor arrangement, notably a flat dynamic X-ray detector (FDXD). The light-sensitive and/or X-ray-sensitive sensors (pixels) of the sensor arrangement are arranged in a planar distribution on a substrate ( 1 ), thus forming a sensitive layer ( 20 ). On the top surface of the layer ( 20 ) there is provided a contact point ( 23 ) for each sensor, which contact point is connected to an integrated circuit ( 6 ) via one or more connection layers ( 30, 40 ). A multi-layer, very compact construction is thus obtained in which the electronic evaluation circuitry ( 6 ) is arranged in a planar fashion and parallel to the sensors ( 20 ). Preferably, a respective evaluation circuit in the circuit ( 6 ) is associated with each sensor, resulting in very short paths and also in a reduction of noise.

BACKGROUND OF THE INVENTION

The invention relates to a sensor arrangement which includes a layer oflight-sensitive and/or X-ray sensitive sensors which are arranged in adistributed fashion.

Sensor arrangements provided with two-dimensional, large-area layers oflight-sensitive and/or X-ray sensitive sensors are used notably for thedynamic reproduction of X-ray images in the medical field. Large-areaX-ray sensors of this kind are also referred to as “flat dynamic X-raydetectors” (FDXD). FDXD-like detectors are universal detector componentswhich can be used in a variety of application-specific X-ray apparatus.The applications include not in the least the computed tomography andnuclear medicine.

An FDXD X-ray detector is known, for example, from EP 0 440 282 B1. Thisknown X-ray detector is based on thin-film technology in which anelectrical circuit is formed by deposition of thin layers on asubstrate. In conformity with EP 0 440 282 B1 there is formed a matrixarrangement which consists of photodiodes which briefly conduct anelectric current, because of the absorption of photons, and thin-filmtransistors which enable selective coupling of the respective photodiodeto read-out leads. Amorphous silicon is used as the semiconductormaterial. The arrangement thus obtained constitutes a large-areaphotosensor which can be rendered sensitive to X-rays by depositing anadditional scintillator layer on the light-sensitive photodiodes. Thescintillator layer then absorbs X-ray quanta and converts such quantainto light quanta which can be detected by the photodiodes.

Also known are arrangements which convert X-rays directly into electricsignals. For example, DE 40 02 429 A1 describes a sensor matrix which ismanufactured by means of the thin-film technology and in which storagecapacitances on a thin-film plate are used instead of photodiodes and adirectly converting material is used instead of the scintillator layer.

In all known FDXD-like sensors, integrated circuits such as, forexample, CMOS circuits, are connected at the edge of the large-areathin-film electronics, said circuits serving for the row-wise driving ofthe matrix cells and for the column-wise amplification and acquisitionof the signals from the matrix cells. It is a drawback that theso-called “switching noise” during the row-wise reading out of thematrix and the long connection leads between the individual sensors andthe circuits give rise to a comparatively high noise level.

OBJECTS AND SUMMARY OF THE INVENTION

Considering the foregoing it is an object of the present invention toprovide an improved sensor arrangement which comprises a large-areaarray of light-sensitive and/or X-ray sensitive sensors and involvesless signal noise.

This object is achieved by means of a sensor arrangement as disclosed inclaim 1. Advantageous embodiments are disclosed in the dependent claims.

The proposed sensor arrangement includes a layer of two-dimensionallydistributed light-sensitive and/or X-ray sensitive sensors, each ofwhich comprises at least one contact point. On this layer of sensors,and parallel thereto, there is arranged at least one component with anintegrated circuit which is preferably formed by means of thesemiconductor technique, which component is connected to said contactpoints and is arranged to read out the sensor signals. The sensorarrangement is preferably a large-area arrangement, meaning that ittypically comprises several thousands of individual sensors and occupiesa surface area of the order of magnitude of from some square centimetersto several hundreds of square centimeters. The contact points formed onthe sensors are preferably all situated on one side of thetwo-dimensional sensor arrangement, even though this is not absolutelynecessary. Furthermore, between the sensor layer and the integratedcircuits there is provided at least one connection layer which containselectrical leads connecting the integrated circuits to the contactpoints of the sensors and/or to external terminals. The externalterminals may notably be voltage supply terminals.

The proposed sensor arrangement has an essentially two-level structure,the first level containing the layer of light-sensitive and/or X-raysensitive sensors whereas the second level, extending parallel to thefirst level, contains the components with the integrated circuits. Forthe sake of brevity the components with the integrated circuits willalso be referred to as “integrated circuits” hereinafter. Because of thedescribed two-level construction, the connections from the individualsensor elements to the read-out electronic circuitry need not be routedacross the entire surface as far as the edge, but may extendperpendicularly to the layer of sensor elements, that is, along theshortest path to the integrated circuits which neighbor the sensors andextend parallel thereto. An arrangement of this kind offers theadvantage of short connection paths, resulting in a reduction of noisein the signals. Furthermore, it is also possible to provide each sensorwith its own “pixel electronic circuitry”.

From a geometrical point of view the circuit arrangement also has theadvantage that it enables a very compact construction of the large-areasensor, including the integrated circuits. More integrated circuits thanallowed by the present state of the art can now be used, because theentire surface area is now available and not only the edge of thesensors, be it that on the other hand it is not necessary either to fillthe entire surface with integrated circuits.

Because of the one or more connection layers, the sensors can beconnected to the integrated circuits with adapted connection distances.Consequently, the terminals of the integrated circuit need not besituated geometrically exactly over the sensors while the advantage ofshort lead paths is preserved nevertheless. Furthermore, using theconnection layers, the requirements imposed as regards the precision ofalignment during mounting can be kept within moderate limits for theconnection technique used, for example, the bump bond technology.

The integrated circuits of the sensor arrangement are preferably formedby means of the CMOS technology. This is an established and time-testedsemiconductor technique which enables operation with small supplyvoltages.

The connection layer may include at least one electrically insulatinglayer wherethrough vias of an electrically conductive material extend.The insulating layer provides electrical separation of the electricleads from the surface of the sensor layer, thus offering more freedomin respect of the routing of such leads.

Preferably, the connection layer is permanently connected to the sensorlayer. This can be realized notably by direct deposition of theconnection layer on the sensors and their contact points, so that theconnection layer and the sensor layer contact one another over a largearea and are connected to one another by material retention.

The distance between the contact points of neighboring sensors in theproposed sensor arrangement may differ from the distance between theterminals of the integrated circuit which are associated with thecontact points. The contact points may notably be situated at a distancewhich is larger than that between the associated terminals of theintegrated circuit. The adaptation of the various distances, which mayalso be referred to as “fan-in” or “fan-out”, is in this case providedby the connection layer. The possibility of such adaptation enables anoptimum choice of the distances between the contact points on the oneside and the distances between the terminals on the other side, that is,in respect of the sensors or the integrated circuits. Notably theintegrated circuits formed, for example, by means of the CMOStechnology, may be reduced to minimum dimensions.

The light-sensitive and possibly also the X-ray sensitive sensors areformed on a substrate preferably by means of the thin-film technique.The connection layer can also be advantageously formed by means of thethin-film technique. According to the thin-film technique which is knownfrom the state of the art, materials for forming resistors, capacitors,conductor tracks and the like are deposited by vapor deposition ordusting while utilizing masks. Moreover, additional process steps suchas etching may be carried out. As a result of the formation of thesensor pixel matrix in such a large-area process, the contact pointshave a suitable mechanical precision. Consequently, the position of thepixels is determined exactly; this is important for correct imaging.

The formation of the sensor arrangement in accordance with the inventionenables a high yield to be obtained for the complete arrangement,because on the one hand the large-area sensor layers are structured verysimply and coarsely and on the other hand the integrated circuits haveconventional dimensions and can be tested in advance. If desired, suchintegrated circuits may also be individually replaced should theyexhibit a defect. The mounting of the integrated circuit on theconnection layer can be carried out by means of standard methods (forexample, bump bonding) so that it is also comparatively uncritical.

The sensors may notably be sensitive to X-rays and hence consist of amaterial which converts X-rays directly into electric signals. Thismaterial may be, for example, germanium (Ge), amorphous selenium (Se),gallium arsenide (GaAs), cadmium telluride (CdTe), cadmium zinctelluride (CdZnTe), lead oxide (PbO), lead iodide (PbI₂) and/or mercuryiodide (HgI₂). Directly converting sensors offer the advantage thatsignal errors and noise as induced by additional converting steps areavoided.

Alternatively, the sensors may also be sensitive to X-rays and have atwo-level structure of an X-ray sensitive scintillation layer and alight-sensitive photolayer. In sensors of this kind X-ray quanta areconverted in the scintillation layer so as to form light quanta whichcan subsequently be detected in the light-sensitive photolayer.

The sensors in the latter structure may notably include photodiodes inthe light-sensitive photolayer, which diodes are advantageouslyphotodiodes of amorphous silicon (Si).

The distribution of the sensors throughout the layer thus formed in thesensor arrangement is preferably shaped as a grid, that is, inconformity with a regular, periodic pattern. The arrangement may notablybe a hexagonal grid and/or a matrix, that is, a rectangular grid withrows and columns. The grid is subdivided into cells, exactly oneintegrated circuit being associated with each of said cells. The largenumber of typically several thousands of individual sensors is thussubdivided into smaller groups of sensors which are situated in arespective common cell, all sensors of such a cell then being connectedto the same integrated circuit. Such a modular decomposition of theentire sensor layer offers the advantage that the surface area of theintegrated circuits may be smaller than the surface area occupied by theassociated sensors while at the same time short connection paths arestill maintained, because the excess surface area of the sensors thusarising is uniformly distributed (in the form of a grid) across theentire sensor arrangement. Furthermore, a sensor arrangement of thiskind is better protected against failures, because the failure of anintegrated circuit can concern no more than one cell of the gridarrangement and not the entire grid. If necessary, an individualintegrated circuit may also be replaced for repair.

In the latter grid-like arrangement of the sensors, preferably betweenapproximately 1000 (one thousand) and approximately 100,000 (one hundredthousand), but notably preferably between 10,000 (ten thousand) and100,000 (one hundred thousand) individual sensors are arranged in acell, all of said sensors being associated with a single integratedcircuit. For such numbers an optimum compromise is achieved between thedistribution of the read-out electronic circuitry among as few aspossible integrated circuits and the need for as short as possibleconnection paths.

In conformity with a preferred embodiment of the sensor arrangement, arespective read-out electronic circuit is associated with each sensor.Said read-out electronic circuit may form part of an integrated circuitwhich comprises a plurality of such read-out electronic circuits forseveral sensors. Because of the direct connection of each sensor to theassociated integrated read-out electronic circuit, the sensors need nolonger be addressed by way of row and column addresses. The switchingnoise induced by such addressing operations is thus eliminated. Afurther advantage of the direct and permanent connection of each sensorto an associated read-out electronic circuit consists in that theread-out speed is higher than that achieved by addressed reading out.Furthermore, with each sensor (pixel) there may be associated arespective read-out circuit with for each sensor a respectivepreamplifier, enabling complex signal processing such as, for example,energy detection, counting, event-controlled reading out, dosedetection, frame transfer and the like.

The invention also relates to an imaging device which is characterizedin that it includes a sensor arrangement of the kind set forth. Thisdevice may notably be an X-ray examination apparatus, a computedtomography apparatus and/or a nuclear medical examination apparatus.

BRIEF DESCRIPTION OF THE DRAWING OBJECTS

The invention will be described in detail hereinafter, by way ofexample, with reference to the FIGS. Therein:

FIG. 1 is a diagrammatic representation of the layer-like structure of asensor arrangement in accordance with the invention which includes aconnection layer;

FIG. 2 shows diagrammatically the layer-like construction of a sensorarrangement in accordance with the invention which includes twoconnection layers;

FIG. 3 is a plan view of a sensor arrangement in accordance with theinvention which includes 16 integrated circuits which are matrix-likedistributed in cells.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a diagrammatic side elevation of a part of a first sensorarrangement in accordance with the invention. The present exampleconcerns a large-area X-ray detector which can be used notably formedical applications.

The entire sensor arrangement is built up on a substrate 1 of, forexample, glass. The structure of this sensor arrangement is in principlea three-layer structure with three different layers which are arrangedon one another and extend parallel to the substrate 1. The first layer20 is the signal generating layer which absorbs incident photons(incident from below in FIG. 1) which are converted into electricsignals such as, for example, charge signals. The connection layer 30which is arranged over the signal generating layer 20 establisheselectrical connections between individual sensors (pixels) in the layer20 and an electronic evaluation circuit. The evaluation circuit formsthe third layer and consists of “two-dimensional” CMOS components 6 ofintegrated circuits which are arranged on and in contact with theconnection layer 30.

The signal generating layer 20 itself has a three-layer structure; atthe bottom and in contact with the substrate 1 there is formed a flatrear contact 21 which serves notably as an electrode which receives agiven, externally applied potential. The light-sensitive and/or X-raysensitive structure 22 is arranged over and in contact with the rearcontact layer 21. The construction of layers of this kind is known inprinciple and is described, for example, in DE 40 02 429 A1 or in DE 4227 096 A1. The layer 22 may notably consist of a directly convertingmaterial such as a-Se, PbO, PbI₂ or the like. Alternatively, the sensorlayer 22 may consist of a photodiode, for example, a PIN photodiode madeof amorphous silicon. In that case the entire structure (with theexception of the integrated circuits 6) can be manufactured by means ofa conventional a-Si thin-film process.

The pixel contacts 23 are provided in the form of a matrix-like grid onthe light-sensitive and/or X-ray sensitive layer 22. These contacts areplanar elements of an electrically conductive material, notably metal.The signal of a single light-sensitive and/or X-ray sensitive sensor(pixel) can be derived from the respective pixel contacts 23.

The connection layer 30 is provided directly on the light-sensitiveand/or X-ray sensitive layer 22 and encapsulates the pixel contacts 23by means of a passivation layer 31. Pixel connections 32 which contact arespective pixel contact 23 and form a contact point on the surface ofthe passivation layer 31 extend through the passivation layer 31. On thesurface of the passivation layer 31 there are provided additionalconnection leads 33 which extend, for example, from the integratedcircuits to the edge of the sensor arrangements where they may beconnected to the supply voltage.

Finally, over the connection layer 30 there is provided the layer withthe integrated circuits (ICs) 6. The individual integrated circuits 6are electrically connected to the pixel connections 32 or the otherconnection leads 33 via a contact material 5 which may be indium bumpbonds.

The arrangement of the large-area signal generating layer 20, theconnection layer 30 and the integrated circuits 6 provided thereonresults in a very compact construction of the large-area sensor. Overalla larger number of circuits can be accommodated because, as opposed tothe present state of the art, not only the edge around the sensors isavailable for this purpose. The individual pixels which are presentunderneath the pixel contacts 23 are preferably connected directly andpermanently to a respective associated circuit, notably an associatedpreamplifier, in the integrated circuit 6. The noise of the pixelelectronic circuitry is thus drastically reduced (switching noise andlong connections are eliminated). Furthermore, intelligent pixelelectronic circuitry can be implemented, comprising signal processingwith energy detection, counting, event-controlled reading out, dosedetection, frame transfer and the like.

FIG. 2 shows an alternative structure of a sensor arrangement. Thisstructure deviates from that of FIG. 1 in that a further connectionlayer 40 is arranged over the first connection layer 30. The integratedcircuits 6 are provided on said second connection layer 40. Thereference numerals and the elements characterized thereby correspond tothose of FIG. 1, and the second connection layer 40 comprises, analogousto the first connection layer 30, a passivation layer 41, pixelconnections 42 and additional connection leads 43 on its surface. One ofthe connection layers may accommodate the supply voltage leads andfurther leads to and from the integrated circuits and be connected, forexample, to bond pads at the edge of the sensor arrangement. As is shownin the FIG., the second connection layer 40 may be used, in addition tothe first connection layer 30, to transform the matrix-like distributionof pixel contacts 23 into a different, preferably spatially denserdistribution of pixel connections 42 (fan-in). Such a denser pattern ofpixel connections 42 is then suitable for the contacting by theintegrated circuits 6. Furthermore, in the second connection layer 40there may be provided further electrical connections so that morefreedom exists as regards the routing of connections.

The sensor arrangements shown in the FIGS. 1 and 2 can be realized bymeans of known technologies, that is, on the one hand by the large-areaproduction of layers 20 and connection layers 30 and 40, for example, asknown from the thin-film technology, and on the other hand by means ofknown connection techniques customarily used for integrated circuits,notably the so-called bump bonding.

FIG. 3 is a plan view of a complete sensor arrangement, that is a viewtaken while looking at the integrated circuits 6. The FIG. shows thelight-sensitive and/or X-ray sensitive layer 20 which consists ofindividual sensors and on which the connection layer with the pixelconnections 32 is provided. The pixel connections 32 again lead to theintegrated circuits (ICs) 6 and couple these circuits to the individualsensor elements. Furthermore, on the surface of the connection layerthere are provided connection leads 43 which lead from the ICs 6 toexternal terminals for a supply voltage.

As can also be seen in FIG. 3, the entire sensitive surface 20 isoccupied by sensors or pixels in a matrix-like arrangement, the numberof sensor pixels on the entire surface amounting to 512×512 in theexample shown. The pixel pitch amounts to 200 μm (the term pitch is tobe understood as the distance of recurrence of similar structures) andthe dimensions of the active surface are approximately 10×10 cm². Thematrix of 512×512 sensor pixels is (logically) subdivided into 16sub-matrices or cells, with each cell there being associated exactly oneintegrated circuit 6 which is arranged centrally on the cell. The numberof pixel channels per integrated circuit 6 thus amounts to 128×128 andthe bond pitch amounts to, for example, 80 μm (=pixel pitch in the IC).

The surface area of the integrated circuits 6, preferably formed bymeans of the CMOS technology, is smaller than the active surface area ofthe sensors. In the present embodiment the ratio of the surface area ofthe ICs 6 to the active surface area of the sensors amounts to80²/200²=0.16 (to approximately 20% with additional connections etc.).For a given cell geometry, this factor also remains constant for largersensor surface area with, for example, 2048×2048 pixels.

1. A sensor arrangement comprising: a layer of sensors arranged in adistributed fashion, said layer of sensors being sensitive to X-rays,each sensor including a pixel contact; an integrated circuit containingread-out electronic circuits and being disposed parallel to said layerof sensors, each read-out electronic circuit being configured to readout a signal from a sensor of said layer of sensors, wherein individualsensors of said layer of sensors are associated with correspondingread-out electronic circuits of said integrated circuit; and aconnection layer provided in between said layer of sensors and saidintegrated circuit, said connection layer (i) being disposed directly onsaid layer of sensors to define a surface, (ii) contains, for eachsensor of said layer of sensors, at least one pixel connection disposedat said surface, wherein the at least one pixel connection iselectrically coupled through the connection layer to the pixel contactof a corresponding sensor of said layer of sensors, (iii) containselectrical leads arranged between said layer of sensors and saidintegrated circuit configured to couple supply voltage connections ofsaid integrated circuit to external terminals proximate an edge of thesensor arrangement, and (iv) electrically connects a read-out electroniccircuit of the integrated circuit to a pixel connection from among saidat least one pixel connection.
 2. A sensor arrangement as claimed inclaim 1, wherein the connection layer includes at least one electricallyinsulating layer and wherein the at least one pixel connectionelectrically couples through the connection layer to the pixel contactof a corresponding sensor of said layer of sensors using vias comprisingan electrically conductive material.
 3. A sensor arrangement as claimedin claim 1, wherein the connection layer is permanently connected tosaid layer of sensors.
 4. A sensor arrangement as claimed in claim 1,wherein the integrated circuit includes terminals associated with pixelcontacts of the sensors of said layer of sensors by way of said pixelconnections, a distance between said pixel contacts exceeding a distancebetween the associated terminals.
 5. A sensor arrangement as claimed inclaim 1, wherein said layer of sensors and the connection layer areconstructed using thin-film technology.
 6. A sensor arrangementcomprising: a layer of sensors arranged in a distributed fashion, saidlayer of sensors being sensitive to X-rays, each sensor including apixel contact; an integrated circuit containing read-out electroniccircuits and being disposed parallel to said layer of sensors, eachread-out electronic circuit being configured to read out a signal from asensor of said layer of sensors, wherein individual sensors of saidlayer of sensors are associated with corresponding read-out electroniccircuits of said integrated circuit; and a connection layer provided inbetween said layer of sensors and said integrated circuit, saidconnection layer (i) being disposed directly on said layer of sensors todefine a surface, (ii) contains, for each sensor of said layer ofsensors, at least one pixel connection disposed at said surface, whereinthe at least one pixel connection is electrically coupled through theconnection layer to the pixel contact of a corresponding sensor of saidlayer of sensors, (iii) contains electrical leads arranged between saidlayer of sensors and said integrated circuit configured to couple supplyvoltage connections of said integrated circuit to external terminalsproximate an edge of the sensor arrangement, and (iv) electricallyconnects a read-out electronic circuit of the integrated circuit to apixel connection from among said at least one pixel connection, whereinthe sensors comprise a material which converts X-rays directly intoelectrical signals.
 7. A sensor arrangement as claimed in claim 1,wherein the sensors have a two-layer structure comprising an x-raysensitive scintillation layer, and a light-sensitive photolayer.
 8. Asensor arrangement as claimed in claim 7, wherein said light-sensitivephotolayer comprises a photodiode.
 9. A sensor arrangement as claimed inclaim 1, wherein the sensors are arranged in a grid, wherein the grid issubdivided into cells, wherein said sensor arrangement further comprisesa number of integrated circuits, each integrated circuit having read-outelectronic circuits, and wherein exactly one integrated circuit isassociated with each cell.
 10. A sensor arrangement as claimed in claim1, wherein the read-out electronic circuit of the integrated circuitassociated with each of said sensors comprises a respective read-outelectronic circuit that includes a preamplifier for each respectivesensor.
 11. An imaging device for performing medical investigationsand/or examinations, which includes a sensor arrangement as claimed inclaim
 1. 12. The sensor arrangement of claim 1, wherein said integratedcircuit further comprises a number of integrated circuits, eachintegrated circuit containing a respective read-out electronic circuitconfigured to read a signal from a sensor of said layer of sensors. 13.The sensor arrangement of claim 1, wherein the connection layerencapsulates the pixel contacts.
 14. A sensor arrangement comprising: alayer of sensors arranged in a distributed fashion, said layer ofsensors being sensitive to X-rays, each sensor including a pixelcontact; an integrated circuit containing read-out electronic circuitsand being disposed parallel to said layer of sensors, each read-outelectronic circuit being configured to read out a signal from a sensorof said layer of sensors, wherein individual sensors of said layer ofsensors are associated with corresponding read-out electronic circuitsof said integrated circuit; a first connection layer provided in betweensaid layer of sensors and said integrated circuit, said first connectionlayer (i) being disposed directly on said layer of sensors to define asurface, (ii) contains, for each of sensor of said layer of sensors, atleast one first pixel connection disposed at said surface, wherein theat least one first pixel connection is electrically coupled through thefirst connection layer from a pixel contact of a corresponding sensor ofsaid layer of sensors, and (iii) electrically connects a read-outelectronic circuit of the integrated circuit to a first pixel connectionfrom among said at least one first pixel connection; and a secondconnection layer provided in between said layer of sensors and saidintegrated circuit, said second connection layer (i) being disposeddirectly on said first connection layer to define a second surface and(ii) containing, for each of said sensors, at least one second pixelconnection disposed at said second surface, wherein the at least onesecond pixel connection is electrically coupled through the secondconnection layer to a corresponding pixel connection of the at least onefirst contact structure, (iii) contains electrical leads arrangedbetween said layer of sensors and said integrated circuit configured tocouple supply voltage connections of said integrated circuit to externalterminals proximate an edge of the sensor arrangement, and (iv)electrically connects a read-out electronic circuit of the integratedcircuit to a second pixel connection from among said at least one secondpixel connection.
 15. A sensor arrangement as claimed in claim 6,wherein the material is constructed from at least one of the following:Ge, amorphous Se, GaAs, CdTe, CdZnTe, PbO, PbI₂ and HgI₂.